API: Not used tag exists in the db, but is not returned in API GET /api/tags result.

[Rurik19]

Issue details

After DELETE /api/entries/{entry}/tags/{tag}.{_format} tag rests in the db (I think that is OK), but after,
in GET /api/tags.{_format} result it doesn't exists. I think it would be useful to have it there (for autocomplete in my chrome ext :) )

Environment

• wallabag version (or git revision) that exhibits the issue: 2.0.6
• How did you install wallabag? Via git clone
• Last wallabag version that did not exhibit the issue (if applicable): >2
• which storage system you choose at install MySQL